Computers, fax machines, printers and other electronic devices are routinely connected by communications cables and connectors to network equipment and/or to external networks such as the Internet. FIG. 1 illustrates a communications system 10 in which a computer 20 that is located in a work area 12 of a building is connected to network equipment 80, 90 using conventional communications cables and connectors. As shown in FIG. 1, the computer 20 is connected by a patch cord 30 to a communications jack 40 that is mounted in a wall (not shown) using a wall plate 42. The patch cord 30 comprises a communications cable 32 that contains a plurality of individual conductors (e.g., insulated copper wires) and communications plugs 34, 36 that are attached to the respective ends of the cable 32. The communications plug 34 is inserted into a communications jack (not pictured in FIG. 1) that is provided in the computer 20, and the communications plug 36 inserts into a plug aperture in the front side of the communications jack 40. The blades of communications plug 36 mate with respective contacts of the communications jack 40 when the communications plug 36 is inserted into the plug aperture of jack 40. The blades of communications plug 34 similarly mate with respective contacts of the communications jack (not pictured in FIG. 1) that is provided in the computer 20.
The communications jack 40 includes a back-end wire connection assembly that receives and holds conductors from a so-called “horizontal” cable 50. As shown in FIG. 1, each conductor of horizontal cable 50 is individually pressed into a respective one of a plurality of slots provided in the back-end wire connection assembly of jack 40 to establish mechanical and electrical connection between each conductor of cable 50 and the communications jack 40. The other end of each conductor in cable 50 may be connected to, for example, the back end wire connection assembly of a connector port 62 of a patch panel 60 that is located in a computer room 14. A first plug of a patch cord 70 may be inserted into the connector port 62, and a second plug 72 of the patch cord 70 may be inserted into a connector port 82 of a network switch 80. The connector port 82 on the network switch 80 may be connected to other network equipment such as, for example, a server 90, via another patch cord 86. The patch cord 30, the communications jack 40, the horizontal cable 50, the connector port 62, and the patch cord 70 provide a plurality of signal transmission paths over which information signals may be communicated between the computer 20 and the network switch 80.
The above-described cables and connectors each include eight conductors that are arranged as four differential pairs of conductors. Information signals are transmitted between the end devices over these differential pairs of conductors rather than over a single conductor using differential signaling techniques. The cascade of cables and connectors that extend between the connector port 82 on the network switch 80 and an end device such as computer 20 is commonly referred to as a “channel” or as a “link segment” 16. Each link segment 16 thus has four differential pairs that can carry four separate differential information signals. In these link segments 16, when a plug mates with a jack, the proximities and routings of the conductors and contacting structures within the jack and/or plug can produce capacitive and/or inductive couplings. Moreover, since four differential pairs are bundled together in each cable, additional capacitive and/or inductive coupling may occur between the differential pairs within each cable. These capacitive and inductive couplings in the connectors and cabling give rise to a type of noise that is called “crosstalk.”
“Crosstalk” in a communication system refers to unwanted signal energy that is induced onto the conductors of a first “victim” differential pair from a signal that is transmitted over a second “disturber” differential pair. The induced crosstalk may include both near-end crosstalk (NEXT), which is the crosstalk measured at an input location corresponding to a source at the same location (i.e., crosstalk whose induced voltage signal travels in an opposite direction to that of an originating, disturber signal in a different path), and far-end crosstalk (FEXT), which is the crosstalk measured at the output location corresponding to a source at the input location (i.e., crosstalk whose signal travels in the same direction as the disturber signal in the different path). Both types of crosstalk comprise an undesirable noise signal that interferes with the information signal on the victim differential pair.
Crosstalk that arises between two differential pairs that are part of the same link segment is typically referred to as “internal” crosstalk. Because communications cables are often bundled together for routing through the walls, floors and/or ceilings of buildings and/or because communications connectors are often located in very close proximity to each other in, for example, patch panels and switches, crosstalk may also occur between one or more differential pairs of a first link segment and one or more differential pairs of a second link segment. Such crosstalk between differential pairs of different link segments is typically referred to as “alien” crosstalk.
Techniques have been developed for reducing the amount of internal and alien crosstalk that is present so that higher data rate signals may be transmitted over the above described link segments. In the mid- to late-1990s, so-called “Category 5E” cables and connectors were developed that could operate at frequencies of up to 100 MHz and support data rates of up to 1000 Mbps for channel lengths of up to 100 meters. Such communications are commonly referred to as 1000Base-T communications. As crosstalk compensation techniques were improved, higher performance “Category 6” cables and connectors were introduced that were designed to operate at frequencies of up to 250 MHz and to support data rates of up to 10 Gbps, although only for shorter channel lengths (e.g., 37-55 meters). These higher data rate communications are commonly referred to as 10GBase-T communications. More recently, even higher performance “Category 6A” cables and connectors were introduced that were designed to operate at frequencies of up to 500 MHz, and to support 10GBase-T communications (10 Gbps) for channel lengths of up to 100 meters.
There are a large number of installed communications systems that use Category 5E or Category 6 connectors and cables. As user demand for higher data rates continues to increase with the proliferation of, for example, video streaming and high definition video, in some cases the hard-wired communications system may be a choke point that slows down data delivery to the user. In an effort to improve performance without the need to replace the large installed base of cabling and connectors, it has been proposed that existing communications systems can be tested and the link segments that will support higher data rates can be identified and thereafter used at the higher data rates.